In technical circles a pitch tube denotes a guide duct in a wind turbine, such that at least part of the guide duct extends at least in part through a rotor shaft of the wind turbine. The rotor shaft connects a rotor, comprising a rotor hub and wind-driven rotor blades, in a rotationally fixed manner to an input shaft of a transmission. The pitch tube extends coaxially with the rotational axis of the rotor shaft or rotor, that is to say, the pitch tube is rotationally symmetrical relative to a rotation axis that extends along the rotational axis of the rotor shaft or rotor, i.e. that is identical to the rotational axis of the rotor shaft or rotor.
To be able to adjust the blade angle (pitch adjustment), electric leads are needed which run between the rotor and a connection terminal on the generator side. Among other things the pitch tube serves to guide these leads through the rotor shaft.
The pitch tube can also be used to supply oil to a transmission of the wind turbine. For example, DE 10 2011 119 471 A1 proposes a double-walled pitch tube having an outer and an inner tube. The hollow space formed between the inner tube and the outer tube in this case serves to convey lubrication oil to the transmission. The electric leads run through the inner tube.
FIGS. 1 and 2 show a system known from the prior art for integrating a pitch tube 101 in a transmission of a wind turbine. FIG. 1 illustrates a rotor-side fixing method for the pitch tube 101. The pitch tube 101 is passed through an opening in a planetary carrier 103 driven by the rotor. To couple the pitch tube 101 to the planetary carrier 103, a connection piece 105 is provided. This has a flange 107 which is bolted to the planetary carrier 103. To prevent oil from leaking out from the transmission between the pitch tube and the connection piece 105, the pitch tube is provided with two all-round grooves 109 in each of which an O-ring 111 is set. The O-rings 111 seal the pitch tube 101 relative to the connection piece 105. In addition the pitch tube 101 is formed with a slot-shaped recess 113. In this recess there engages a securing strip 115 attached to the connection piece 105. Thereby, a rotationally fixed connection is formed between the pitch tube 101 and the planetary carrier 103. In particular, the pitch tube 101 and the planetary carrier 103 are connected in a rotationally fixed manner. Accordingly, the pitch tube 101 rotates along with the rotor.
FIG. 2 shows the generator-side end of the pitch tube 101 opposite to the rotor-side end thereof shown in FIG. 1. On the generator side the pitch tube 101 passes through a housing 201 of the transmission. Since the pitch tube 101 rotates along with the planetary carrier 103 whereas the housing 201 is fixed, the pitch tube 101 is mounted to rotate in the housing 201 by virtue of a bearing 203. A locking ring 205 attached to the housing 201 and a locking ring 207 attached to the pitch tube 101 fix the bearing 203 in the axial direction. A sealing ring 209 prevents oil from leaking out of the transmission between the housing 201 and the pitch tube 101.
In the system described strict demands are made on the dimensional accuracy of the pitch tube 101. On the one hand the gap between the pitch tube 101 and the connection piece 105 has to be very narrow. Otherwise, the sealing action of the O-rings 111 would be insufficient, so that oil could escape from the transmission through the gap. On the other hand, at its generator-side end the pitch tube 101 serves as a bearing seat. Accordingly, the outer diameter of the pitch tube at that point must maintain as accurately as possible an oversize relative to the diameter of the inner race of the bearing, as required for a bearing seat.
The electrical leads running through the pitch tube 101 also rotate together with the pitch tube 101. Thus a coupling is needed, in order to connect the rotationally fixed leads on the generator side with the rotating leads in the pitch tube 101. Accordingly, the pitch tube 101 must be designed at its generator-side end in such manner that it can be connected to the coupling As a rule, the connection on the generator side also has to comply with specifications issued by the equipment manufacturer.